An employer can make the SEP contribution to any SEP-IRA owned by the employee, so the S corp can make its SEP contributions to the same SEP-IRA as you did as sole proprietor.
If the S corp uses a calendar tax year, the due date of a 2021 Form 1120-S was March 15, 2022 and it's now too late to request a filing extension. If no request for a filing extension (Form 7004) was made by March 15, this S corp can't make a SEP contribution for 2021. Filing Form 7004 by March 15 would have extended the filing deadline to September 15.
